Next week, the Republican National Convention will choose Donald Trump to be its nominee for the third presidential election cycle in a row. Between then and now, Trump will also choose his vice president. No one can know Trump's mind for certain, but he is believed to have settled on three finalists: Sen. J.D. Vance (R–Ohio), Sen. Marco Rubio (R–Fla.), and North Dakota Gov. Doug Burgum. While the vice presidency is often derided as a relatively unimportant job, there are reasons to think...